Diving gas mixtures and methods of deep diving

ABSTRACT

A breathing gas composition for divers for use at depths of from about 150-850 fsw consisting of oxygen and a three component gas mixture of neon, helium and nitrogen.

United States Patent [19y Schreiner et at.

DIVING GAS MIXTURES AND NETHODS OF DEEP DIVING lnventors: Heinz R. Schreiner, South Salem;

- Robert W. Hamilton, Tarrytown;

Arthur W. Francis, New City, all of NY.

Union Carbide Corporation, New York, NY.

Filed: Apr. 28, 1972 Appl. No.: 248,700

Assignee:

US. Cl. 128/142, .424/366 Int. Cl. A6lk 27/00, A62b 7/02 Field of Search 424/366; 128/142 References Cited UNITED STATES PATENTS ll/l923 Cooke 424/366 June 11, 19.74

10/1927 Yant 424/366 OTHER PUBLlCATlONS William et al., Chem. Abst. Vol. 74 (1971) page Primary Examiner-Sam Rosen Attorney, Agent, or FirmE. Lieberstein 7 Claims, 7 Drawing Figures PATENTEUJUN 1 1 m4 LOSS OF SPEECH EFFECTIVENESS of Velocity of Sound in Air of 0C and I Atmosphere 3.815591 SHEET 2 OF 7 smaooaom sa H) I fin 8 N /EIE)NVH EHI'LLXIW NOBN-WHI'IBH CIHHBddSHd f NOEIN o NQOMIN Nooav I l I l O O O O O O qoeadg qbnoJq uouomunwwog H HE 480 o 640 Velocity of Sound through gaseous medium Meters/second PATENTEDJUH 1 1 @914 HELIUM HYDROGEN F G. 4. 7 LOSS OF WORK EFFECTIVENESS DUE TO BREATHING DIFFICULTY BASED ON A DENSITY- VISCOSITY INDEX SHEET t 0F 7 AlIDVdVI) MHOM TVWHON d0 FEET OF SEA WATER PATENIEDJIIII I I I914 SHEET 5 OF 7 RELATIVE ADVANTAGES OF NEON AND HELIUM COMPONENTS IN I DIVING GAS MIXTURES Showing Increasing percentages of neon from Ieft 1o right,in a mixture of neon and helium, with favorable factors plotted in an upward direction and unfavorable factors plohed downward.

w v m N w E m w N M I E .m w. I M W W M@ w d P G .5 m O W Huh 6 B .m W .mm m I\ 0 6 5 ..J| W N T 8 .H O/\ m d w H r\. C G 5 .M I CI r 7 0;! O 8.0 R d O. ..r\ W m 7. hm u V. B We Q B 3 w m w m e a m .mm.. a H5 WW w m .m, W W f E u N m .w o F 0 m \w c 0 0 m n 0 5 I i 0 W N m 6 N E W 6 mu m g nw 5 T/ .n A Afl 8 Q E U r O R U w m. c E S D m W w MP 0 O 0 W 0 O O O O O 0 4 e NF m w zOmZ @004 m0 ZOFQZDE PATENTEDJUH 1 1 1974 v sum ear 7 on NF WVWHON d0 SSEIN3AllO3dd3 )iHOM 1- DIVING GASMIXTURES AND METHODS or DEEP DIVING This invention relates to. diving gas mixtures for deep diving and to a method of deep diving using such mixtures.

BACKGROUND OF THE INVENTION To sustain life a diver must be supplied breathing gas at "a pressure equal to the pressure in the water surrounding the diver. There is however, an upper limit of oxygen pressure above which the oxygen becomes bio chemically toxic. Thus, it is necessary'to include an oxygen diluent in a divers breathing gas. To satisfy normal breathing requirements at high pressures, it is necessary to supply between 0.2-1.5 atmospheres of oxygen with the balance represented by-a non-toxic diluent. Air of course is a suitable breathing mixture for a diver based primarily on nitrogen as the oxygen diluent. In fact, air is the preferred breathing mixture for all dives to depths of less than about 150-200 fsw (feet of sea water). However, even at 150 fsw, when breathing air most divers feel the effects of nitrogen narcosis. Beyond this depth helium is preferred as the diluentand is in fact particularly well suited to the depth range immediately beyond air diving (e.g., 150-250 fsw). Helium does not cause narcosis at these pressures, is relatively inexpensive and at least .in the United States is readily available. Moreover helium has a low density and is, therefore, easy to breathe at such pressures.

But there are problems for the diver breathing helium, problems that are seriously amplified as diving depths approach those of the outer continental shelves and beyond.

First there is the problem of communication. The destructive effect that breathing helium has on the normal human voice is well known, if not well understood. Due principally, it is believed, to changes in the speed of sound in the gas medium, this effect is a sensitive function of depth. Helium speech at sea level is distorted, in a way that seems funny to both the listener and the speaker, but it is completely intelligible. At 200 fsw helium speech is still reasonably intelligible. However, as depths increase to the range between 400 and 600 fsw the situation becomes more serious, and to the manager trying to get a job done the sound of helium speech is nolonger considered funny. Speech in this range is totally lost on an untrained ear, though anticipated statements can be understood by a listener familiar with the voice and the situation. So often, however, a sudden change in the topic of conversation throws everyone off, and it is necessary for the diver to speak slowly, repeat himself and to try to say things a different way. It can be done but it is slow and consequently expensive.

Another problem of deep diving that is particularly accentuated by the use of helium is that of cold. Even ment is considerably greater than into air. A chilled diver takes much longer to do a given job, is less likely to respond properly to emergencies and probably is more difficult to decompress. Even if the diver could be kept warm long enough to finish his work, a bonechilling sojourn would await him when he returns to the heliox (helium-oxygen) filled diving bell. This is considered by many divers to be more stressful and unpleasant than working in cold water.

Decompression is a problem associated with all deep dives. Although saturation techniques make the continental shelves accessible to' all operators whocommand the requisite resources, this kind of diving-is neither easy nor necessarily economical. In the commerprobably the worst possible gas. Since too little is really known about the biophysics of decompression and decompression sickness it is sufficient to say that no matter what gas is breathed decompression. is a difficult and a slow process, and is probably the most serious problem facing the deep diving operator today.

OBJECTS It is, therefore, the principal object of this invention to provide a gas mixture for deep diving which overcomes the main defects of known diluents and which is safe to use, available, economical, and which offers both practical and theoretical advantages over the use of-helium.

It is a further object of the present invention to provide a neon-based gas mixture which takes advantage of the best properties of neon, helium and nitrogen while minimizing their disadvantages.

It is yet another object of the present invention to provide a method of deep diving using a neon-based diving gas mixture.

Other objects and advantages of this invention will become apparent from the .following detailed description of the invention when taken in connection with the accompanying drawingsin which:

FIG. 2 illustrates the relationship of known diluents and the preferred mixture with respect to loss of speech intelligibility; I

FIG. 3 is a similar illustration-as that of FIGS. 1 and 2, but with respect to body heat loss on work effectiveness;

FIG. 4 is a similar illustration asthat of FIGS. 1-3, but with respect to breathing capability at varying depth;

FIG. 5 illustrates the advantageous and disadvantageous properties of a neon-helium diving gas mixture as a function of increasing neon both substantially with and substantially without the addition of nitrogen;

FIG. 6 illustrates the degree of useful work that can be expected'from varying mixtures of neon and helium, both with and without nitrogen at 850 fsw; and

FIG. 7 illustrates a preferred decompression profile for the gas mixture of the present invention.

mercial diving situations. There are no situations indicated for total loss of speech communication since between well trained personnel some limited comprehcnsion is retained in the face of the most severe distortion. It is similarly difficult to evaluate the effect of body heat loss on work effectiveness. A man may continue to perform some useful work even when he is miserably TABLE r-cMaAi1A'rrvE PROFERTIES 0F SUGGESTED GASES FOR use IN oivii Properties Argon Nitrogen Neon Helium Hydrogen Decompression Not good-can only Good in short dive; Fairly easy to elim- Easily eliminated About the same as be used under slow return from inate in long dive from body in long He. special'circumlong dives. builds up slowly dives; builds up stances. in short dive. fast in short dive. Narcosis Narcotic in nominal Narcotic beyond No narcosis No narcosis Slight narcosis at diving range. about 200 fsw. great depths. Voice distortion... Makes voice deep.... Normal Nearly normal Large distortion Large distortion. Thermal conductiv Good insulation Fair to good Fair insulation Poor insulation Very poor insula A insulation. tron. Breatheability Hard to breathe Hardto breathe at Relatively hard to Can be breathed to Same as He.

- depth. Low cost, readily Cost and worldwide availavailable.

ability.

' "nia'os eeirvs"ar'coanirearai military diving is th e accomplishment of useful work at the working depth. Useful work can be inhibited by several factors resulting from the choice of diluent gas. These inhibitions to useful work include:

1. Reduced consciousness due to narcotic effects.

2. Reduced intelligibility of voice communications.

3. Fatigue, muscle stiffness and loss of sensory capability from loss of body heat. 4. Work capacity limitations resulting from breathing difficulty.

The above factors are displayed graphically in FIGS. 1-4. The most severely limiting factor is the narcotic effect displayed in FIG. 1. In its mild stages marcosis results in errors in judgment and observation. In its most severe stage it results in total loss of consciousness. As shown, pure helium or neon exhibit no narcotic effect while pure argon and nitrogen for most of the commercial diving depth range from 150-850 ft. is too narcotic. Narcotic effects appear to be a function of the partial pressure of the narcoticgas. For example, we normally breathe'nitrogen at'a partial pressure of 12 pounds per square inchwithout anyundesirable influ ence. To avoid undesirable narcotic effects throughout the entire depth range encountered in the continental shelf argon should not exceed percent of .the total mixture and nitrogen should not exceed percent.

The impact of reduced speech communication is less easy to evaluate. FIG. 2 displays the relationship of speech intelligibility to the velocity of sound through the gaseous medium. Velocity of sound is influenced primarily by the molecular weight of the gas and secondarily by factors such as temperatureand pressure. The various gases are appropriately indicated for the velocity of sound at 32F and one atmosphere pressure. FIG. 2 indicates reasonably .well the relationships between the gases'at any of the pressure temperature combinations likely to be encountered in actual com- Lowest cost, available' anywhere.

5,000 fsw. Moderate cost,

available only in certain places.

breathe.

High cost, depending on purity; available many P Low cost, readily available.

laces.

cold. It has been objectively determined that loss of body heat does cause accelerated fatigue, loss of sensory perception and muscle stiffness. Various types of clothing and suit heating devices has been developed to combat heat loss in deep diving. However the thermal conductivity of the gaseous atmosphere remains a major factor in heat loss control. FIG. 3 displays the effect of different'gaseous environments on the body heat loss compared to an ir environment. To understand the significance of this display it'is necessary to keep in mind that as lower temperatures are encountered in an air environment, there will be loss of work effectiveness. What FIG. 3 indicates is that by switching to different gases this loss of work effectiveness will be reduced or accentuated depending on the thermal conductivity of the gas chosen to replace normal air. If inened according to the relationships displayed in FIG. 3. Under the "temperature conditions amassed in commercial dividing in the ISO to 850 foot depth range, the use of either hydrogen or helium as the atmo'sphere surrounding the diver will cause a major loss in workeffectiveness compared to normal air. The use of pure neon, as influenced through temperature, will cause only a very minor loss of work effectiveness compared to normal air. Use of an argon atmosphere would result in less loss of work effectiveness than with normal air and therefore in FIG. 3 argon showsa performance above percent compared to normal air.

A fourth influence of gaseous environment on diver work performance concerns breathing difficulty. Breathing must accomplish two separate objectives. First oxygen must be taken into the lungs and thence into the blood stream. Secondly carbon dioxide produced as a result of muscular activity must be removed tion for carbon dioxide removal. To get itout you must breathe it out.

In a human the nervous system responds to increasing levels of carbon dioxide in the blood and it is the primary stimulus to breathing. A person breathing air is a confined space in which carbon dioxide content builds up will encounter difficulty in expelling carbon dioxide from the blood. These difficulties will produce increasing discomfort and distress. Since muscle work produces carbon dioxide thisaccentuates the problem and under normal conditions heavy manual labor is not performed in a confined space unless adequate ventilation is provided to avoid this carbon dioxide build-up.

In diving a similar problem exists. In this case the problem is caused by the increasing difficulty in moving the breathing gas in and out of the lungs as the gas density increases with-increasing depth pressure. At 850 feet of sea water, the pressure is 400 pounds per square inch. Normal air at this pressure has a density of 2% pounds per cubic foot, which is 27 times higher than its normal density. It is difficult to breathe so dense a material. It is difficult to move this many pounds of material in and out of the'lungs every second for any prolonged time period.

In addition to the adverse effect of density the'work of breathing is also influenced by the viscosity of the breathing gas. To relate these two factors the diluent gases are compared based on a density-viscosity indexl The density of pure elemental gases at 70F. at one atmosphere' pressure is readily obtainable from well known sources of literature on thesubject as well as published handbooks. This is also true for viscosity. A density viscosity index is thus readily computed by multiplying the density in lbs. per cubic ft. by the viscosity in poises X FIG. 4 graphically portrays the impact of breathing difficulty on the capacity to do useful work at various depthsof sea water. At nor'rnalatmospheric pressure full work output can be maintained breathing any of these gases as the oxygen diluent. As diving depth-increases, there will be very little, if any, reduction in work capacity until a threshold level is reached.

At such threshold, which varies with different persons,

the body tirstencounters difficulty expelling sufficient carbon cioxide to'keep balance'with the muscular activity rate. To avoid acute distress, the diver must re.- duce his work activity to reduce the carbon dioxide formation. With only a relative small increase in depthbeyond such threshold level, the diver will be forced to curtail his work entirely to prevent carbon dioxide buildup. In FIG. 4 the'fall-off of work capacity is indicated as a band because different individuals have different responses, i.e., different threshold levels, and because other effects such as temperature also contribute to breathing difficulties. v

The 'above discussion has, to this point, been restricted to pure elemental gases. It has been shownthat for diving in the -850 fsw range, the pure elemental gases offer substantial disadvantages. Nitrogen and argon are too narcotic. Helium, which is presently used, distorts the voice, chills the diver and is not readily available. Hydrogen distorts the voice chills the diver and in addition represents a potential fire and explosive hazard. Pure neon becomes hard to breathe at lower depths, thereby increasing the probability of distress.

The decompression, voice distortion, and breatheability characteristics for neon as stated in Table land the effect of neon on loss of work effectiveness as illustrated in FIGS. 2 4 were determined in accordance with the present invention. Historically, the use of neon many that the physical and chemical nature of neon is such that neon was expected to exhibit narcotic properties in deep diving, and that its long term biological effects were unknown and possibly detrimental or dangerous. Furthermore, it was thought, and still is considered by most experts, to be extremely dangerous to attempt to decompress from a dive using neon in the breathing gas.

The present invention is based on the theoretical proposition that although pure neon may indeedbe more difficult to breathe than helium and may posses othe disadvantages, not to mention its cost, its beneficial characteristics should be capableof exploitation in an appropriate combination with helium and/or other gases, even nitrogen, if a diver could be successfully decompressed with'such a mixture. Even then, such a combination would have to demonstrate increasedbenefits for deep diving with the shortcomings of theindividual gases evident to only a minimal extent.

Proof that neon could bebreathed safely and without narcosis :was fundamental before the validity of the above proposition could be established. Fortunately, through experimentation for varied medical purposes a large body of evidence has become available to permit the conclusion that no unfavorable biologicalor narcotic effects exist.

A summary of the data most relevant to biological effects is contained in the following Table II:

TABLE II Biological v System Exposure Findings and (Reference) Neuraspora 35 atm. Neon falls between helium and nitrogen on inhibition scale (Schreiner et al.. Science 136: 653. l962-) C'rarsa Neum'spara' I20 atm. No greater inhibition than 50%;

dose response eurveflat above 35 atm. (Buckheit et al., .I. Bact. 911622, 1966.) Crassa HeLa cells in Neon inhibits growth as a function of pressure less than N, or He. (Robinson et al., Federation Proc. 27:706. 1968.) tissue culture Frog gastro l5 atm. No effect of neon, (Gottlieb et al.'.

Am. J. Physiol. 2082407. 1965.)

cnemius muscle I i i i No detectable narcotic effects.

(Miller et al., Science l57:97, I967.)

Ne wts, mice I25 atm.

II Continued 1 Biological System Exposure Findings and (Reference) Rats, autis l as,

No effect attributable to neon.

(Hamilton et al., SpaceLife Sciences 2:307, 1971.) (and In addition to the cell and animal exposures shown in Table II, a number of experiments have been conducted with human subjects showing that neon can be breathed safely without narcosis'. These experiments were concerned solely. with the pharmacological, physiological and neurological aspects of high pressures of mixtures containing substantially all neon as the inert gas component in the breathing mixture. In no case has any evidence appeared which suggests that there are either immediate or long-term detrimental effects that may result from breathing neon. A summary of the reported experiments and results are given hereinbelow: 1. Ocean Systems 650 FSW Saturation Experiment,

This experiment represented the first exposure of man to saturation diving conditions at continental shelf depths. Two subjects, while saturated with a mixture of a 95 percent helium, 4 percent nitrogen and about 1 percent oxygen breathed a neon-oxygen mixture by.

mask while carrying out two different performance tests and making speech recordings. Psychomotor performance tests demonstrated that no detectable decrement during, neon breathing could be seen; in fact, slight improvement was noted. (Schreiner et al., Federation Proc. 25-(2):230, 1966.) 2. Royal Naval Physiological Laboratory, Neon Performance, 1966.

Using multiplication and a simple test of muscular coordination involving picking up. ball bearings with tweezers, human subjects were exposed by mask to a single neon-helium-oxygen mixture.(65.6 percent, 16.4 percent, l8 percent) at 7 atmospheres (200fsw) and to air at 5.8 atm. (I52 fsw), depths chosen to provide equal partial pressures of the inert gases. Test results showed an appreciable (12-15 percent) decrement in air, while subjects breathing neon showed a 3 percent lower arithmetic score and did just as well if not better on the ball bearing test. (Bennett, P.B., The Atiology of Compressed Air Intoxication and Inert Gas Narcosis. Oxford: Pergamon, 1966.). 3. US. Navy, Pulmonary Function; 1968.

During the laboratory preparation state of the-Sealab Ill operation saturation experiments were conducted by the US. Navy involving exposures-to 600 and 825 fsw pressure equivalent. As part of these experiments neon-oxygen mixtures were breathed by four subjects during a study of pulumonary function. At 825 feet (26 atmospheres) the density of the breathing mixture was 15 times that of sea level air. Under these conditions the subjects were able to move 40-50 liters of gas per minute, in and out of their lungs, enough to do moderate work with some reserve. (Anthonesen, et al.-, ln:

lj'rlderwz lt e r' Physiology, edited jby C. .ljlcamberts en.

Ne k A ad m sss 7 4. Duke University, EEG and Reaction Time with Noon, 1970.

In a saturation experiment primarily devoted to a study of cardiorespiratory parameters, recordings of EEG, reaction time and alpha blocking were made under identical experimental conditions using neon, helium and nitrogen respectively at a pressure equivalentto 200 fsw. No statistically significant differences between neon and helium were seen, but nitrogen caused an'increase in reaction time. All measurements were made under normoxic conditions. (Townsend, et

Withthe knowledge that neon is safe for a diver to breathe, it thus became possible to determine whether neon could be combined with another gas or gases especially helium to provide an optimum diluent gas composition for deep diving, which would exhibit the preferred characteristicsof each gas taken individually while avoiding their unfavorable properties. it also still remained to be established whether a diver could be successfully decompressed with a neon based'gas mixture, and further, what-decompression criteria would be necessary to effect such decompression. It should be understood that it took years to evolve safe and optimum decompression tables for pure helium and such work is in fact still being conducted.

After extensive investigation involving actual dives, examples of which will be given hereinafter, and laboratory studies and experiments the properties of varying mixtures of neon and helium with and without substantial additions of nitrogen and their effect on man in the deep diving environment have been noted. The principal factors as they relate to the list of properties given in Table l have been graphically illustrated in FIG. 5. The known characteristics of helium is used as a comparative reference i.e., represents the zero coordinate. The vertical scale above the zero coordinate displays, in percentage of deviation, conditions favoring a neon-helium mixture over pure helium while below the zero coordinate unfavorable conditions to such a mixture, in percentage of deviation from pure helium, is indicated. The horizontal axis from the zero coordinate, representing pure helium, displays increasside the scope of this disclosure, determine the specific concentration of oxygen at a'particular depth. Hence, for simplicity, the diluent composition will hereinafter be discussed on a percentage scale of 100.

The factors taken into account in preparing FIG. 5 are: 3

a. Thermal conductivity. This property affects the removal of heat from a divers body. As the percentage of neon is increased the thermal conductivity of the mix is reduced. This is shown by an upward-moving curve, indicating that as the percentage of neon in the mixture is increased this property is becoming more favorable.

b. Speech improvement. Based on speech specto grams of second and third formants of vowel sounds,

verbal Communication improves slightly with increasing neon up to about a 50-50 mix and then sharply improves with a further increase of neon leveling off above about 78 percent neon. Subjective observations of neonspeech intelligibility corroborate these data.

c. Roth bubble factors, shown for both blood and fat. Theoretical factors based on physical "properties of the gases and their relation to bubble formation and growth. These factors improve as the percentage of neon increases. (Roth, E.M., NASA SP-l l7, Washington, 1967.) f

d. Solubility in ater and fat. These properties affect the amount of gas gaken up by the body during a dive; they show a slightly increasing gas uptake with increasing percentages of neon in the breathing mixture.

e. Viscosity. Under certain conditions this property makes noen more difficult to breathe than helium, shown as increasingly unfavorable as neon percentage increases f. Cost of neon-heliummixtures. This-curve shows linearly increasing costs as neon admixture increases up to 75-percent, and a sharp rise in cost (downward line) after that. I

g. Density. The linearly increasing density curve represents a mixture of neon and helium.

The dotted curves on the chart relate to-mixtures containing substantial nitrogen above 5 percent:

.h. Estimated cost (with nitrogen). Certain neon mixtures can be obtained at much lower cost if some residual nitrogen in the mixture is acceptable-This curve shows how price is affected as percentage of neon is increased in this type of mixture. This cost curve, becoming increasingly disadvantageous as percentage of neon increases, should be compared with the last (lowest) curve showing density with nitrogen.

Not shown on the graph but of equal importance is the subjective response of divers exposed during deep sea dives to neon based inert gas mixtures. When a diver responds negatively his confidence is impaired affecting his mental state and his willingness to breathe with deliberation. This in turn will affect his coordination, ease of function and reaction time. In general the response was best with a mixture containing below 80 percent neon.-

FIG. 6 illustrates the degree of useful work that can be expected from varying mixtures of neon and helium at 850 fsw.

It is apparent from an analysis of FIGS. 1-6, taking the above noted subjective response into consideration, that an optimum gas diluent composition does in fact exist, for the diving range of 150-850 fsw, consisting of a three component gas mixture of neon, helium and nitrogen in the following concentrations:

Neon 50-8O vol. percent Nitrogen -20 vol. percent Helium Remainder; wherein the volume percentage of helium is-at least equal to that of the nitrogen.

The preferred range for an essentially neon-helium mixture with nitrogen limited to below percent is as follows:

Neon 75 vol. percent (ranging from 72 to about 78 percent) Helium 25 vol. percent (ranging from 28 to 22 percent) When nitrogen is deliberately included the preferred range is as follows:

Neon 65 vol. percent (ranging from 60 to 72 percent) Helium 20 vol. percent (ranging from 18 to 22 p'ercent) Nitrogen 15 vol. percent (ranging from 5 to 20 percent) The above noted preferred ranges should not negate the possible existence of trace concentrations of hydrocent nitrogen, this effect is negligible and will not inhibit the diving operation or disturb the diver. Moreover, although the density of nitrogen is greater than either neon orhelium the viscosity of nitrogen is lower than each of them. Thus, the presence of some nitrogen will not alter the threshold level at which breathing difficulty would be encountered.

It was further discovered pursuant to this invention that decompression following dives using the hereinabove identified optimum mixture is not only possible with state-of-the-art helium decompression procedures, but in fact offers a substantial advantage in terms of the time required for successful decompression and the safety and well-being of the divers undergoing such decompression. Experts in the art of decompression theory would not have assumed it possible to decompress successfully from a neon dive using standard helium decompression tables. Morever, some experts would have considered any attempt to decompress from a neon based gas to be unsafe regardless of procedure.

Twelve comparative dives were carried out using two different divers, first with helium and then with the optimum mixture of the present invention, at corresponding depths applying state of the art helium decompression procedures- The results of these dives are listed below in Table III.

TABLE Ill Bottom Gas-Helium-Oxygen (Standard Mix) Bottom B None Bilateral hip pain at 40 fsw and 600 min. decompression time; treated by recompression to 60 fsw and 0, breathing. Decompression TABLE ill-Continued Bottom Gas- Helium-Oxygen (Standard Mix) Bottom Description Depth Time Diver of Decompression sickness (fsw) (min.)

. rates were reduced to l t'L/min. 600 I 33.1 B Sinus squeeze at 70 fsw and 423 min. decompression time; treated with Tyzine nasal drops and actifed.

Bottom Gas-Optimum Neon Mix; (s N2) and Surprisingly even using helium'tables the decompression results in the above Table III show significantly safer results with the optimum mix then with helium alone.

FIG. 2 shows a decompression profile which has been developed for the preferred neon-helium mixture. The profile was developed to further optimize the characteristics of the optimum mixtures of the present invention in regard specifically to decompression. The procedure was tested to pressure of 680 fsw. This depth is at the outer limits of present diving technology, but is representative of the range of diving in which neonbased gas offers most advantage. The figure shows the time-pressure curve for decompression from thirtyminute working dives in which divers breathed a mixture of 5 percent oxygen combined with an inert gas having about percent neon, less than 5 percent N and remainder helium.

What is claimed is: l. A breathing gas composition consisting of oxygen and a gaseous diluent for use by divers at depths of from about 150-850 fsw, wherein said gaseous diluent comprises a three-component gas mixture consisting essentially of 50-80 VOL-percent neon, less than 20 percent nitrogen and the remainder helium and wherein the volume percent of helium is at least equal to that of the nitrogen.

2. A breathing gas composition as claimed in claim 1 wherein the gas mixture consists essentially of 72 78 percent neon, less than 5 percent nitrogen and the remainder helium.

3. A breathing gas composition as claimed in claim 1 wherein approximately 75 percent neon is present in the gas mixture.

4. A breathing gas composition as claimed in claim 1 wherein the gas mixture consists essentially of 60 72 percent neon, 5 20 percent nitrogen, and the remainder helium.

5. A breathing gas composition as claimed in claim 1 wherein approximately 65 percent neon and approximately 15 percent nitrogen is present in the gas mixture, balance helium. 1

6. In a method for deep sea diving at depths of from 15 0-850 fsw wherein the diver is required to be decompressed during ascent to atmospheric p ressure, the improvement of which comprises:

supplying said diver for inhalation at maximum working pressure and during decompression a gas com position consisting of 0.827.0 vol-percent oxygen, and. 73.0-99.2 vol-percentof a three. component gas mixture consisting essentially of 50 80 percent neon, less than 20 percent nitrogen and the remainder helium, wherein the percentage of helium is at least equal to that of the nitrogen and wherein the relative concentration of oxygen in the total gas composition is varied with depth.v 7. [n a method as claimed in claim 6 wherein decompression is carried out using.conventional'helium decompression tables. 

2. A breathing gas composition as claimed in claim 1 wherein the gas mixture consists essentially of 72 - 78 percent neon, less than 5 percent nitrogen and the remainder helium.
 3. A breathing gas composition as claimed in claim 1 wherein approximately 75 percent neon is present in the gas mixture.
 4. A breathing gas composition as claimed in claim 1 wherein the gas mixture consists essentially of 60 - 72 percent neon, 5 - 20 percent nitrogen, and the remainder helium.
 5. A breathing gas composition as claimed in claim 1 wherein approximately 65 percent neon and approximately 15 percent nitrogen is present in the gas mixture, balance helium.
 6. In a method for deep sea diving at depths of from 150-850 fsw wherein the diver is required to be decompressed during ascent to atmospheric pressure, the improvement of which comprises: supplying said diver for inhalation at maximum working pressure and during decompression a gas composition consisting of 0.8-27.0 vol-percent oxygen, and 73.0-99.2 vol-percent of a three component gas mixture consisting essentially of 50 - 80 percent neon, less than 20 percent nitrogen and the remainder helium, wherein the percentage of helium is at least equal to that of the nitrogen and wherein the relative concentration of oxygen in the total gas composition is varied with depth.
 7. In a method as claimed in claim 6 wherein decompression is carried out using conventional helium decompression tables. 